V.17 ** So, what is the process, how does one come
to the knowledge of the truth?

"...faith comes from hearing, and hearing by the word of Christ..."
Always, salvation comes from hearing and understanding the saving message
of Jesus Christ and not in the intuition, mystical experience, meditation,
speculation, or philosophy of the world's system.

V.18 ** As he continues his concern for Israel's salvation, what
rhetorical question does Paul put forth?

"...surely they have never heard, have they?"

** What is the tragic answer?

Yes they have! Quoting from the Septuagint [Greek] version of Psalm
19:4 Paul says, "Their voice has gone out into all the earth, and
their words to the ends of the world". The voice and words represent
the testimony of the heavens. All of creation was used to witness to
Israel of the power of God and yet they refused to listen and are without
excuse!

V.19 ** How does Paul continue his line of rhetorical questioning?

"...surely Israel did not know, did they?"

** Again, what is the tragic answer?

Yes they did! Some 1500 years prior to the writing of this epistle,
Moses recorded the prophecy that Israel would become jealous over the
Gentiles receiving the salvation (Deuteronomy 32:21) that they had mistakenly
thought belonged to only them.

V.20 ** Isaiah also spoke boldly about the Gentiles coming to
salvation by God's grace, how do we know it was not because of our own
effort?

Because Isaiah said that we "sought" not after God and "did
not ask" for a relationship with God!

V.21 ** The mercy and grace of God to offer the "good news"
to the Gentiles is unfathomable by those of us who have been saved through
faith in Christ. Equally difficult to grasp, is the tragic error of the
nation of Israel who failed to receive God on His terms, but instead reduced
His glory to a set of rules that they could keep. What was the heart of
the problem?

The nation of Israel was made up of a "disobedient" and "obstinate"
people.